1. Field of the Invention
The present invention relates to driving circuits of light emitting devices, and more particularly, to a driving circuit of a light emitting device that has a simplified configuration by using one comparator to detect an over voltage generated when a light emitting device is opened, and an over voltage applied to a current source to thereby facilitate the implementation of an integrated circuit.
2. Description of the Related Art
In general, cold cathode fluorescent lamps (CCFL) are used as light sources of backlight units of LCD TVs. Recently, backlight units that use light emitting diodes (LEDs) as light sources have been actively developed.
An LED is generally driven by two methods. One is a switching method by which a switching converter is used to perform voltage conversion for an LED array and control a constant current. The other is a linear method by which a switching converter is used for voltage conversion, and a saturation region of a transistor or a FET is used as a constant current source.
However, in a case of the linear method, which is known to be more cost-efficient than the switching method, a complicated feedback circuit needs to be simplified to increase the efficiency of the constant current switching converter.
A driving circuit of an LED using the linear method according to the related art will be described in brief. According to the related art, the driving circuit includes an LED block as a light source, a DC/DC converter block supplying a driving voltage used to drive the LED, a constant current block causing a predetermined amount of current to flow through the LED, and a feedback block.
The feedback block of the DC/DC converter includes a first feedback circuit and a second feedback circuit. The first feedback circuit detects a voltage by dividing resistance in order to detect the opening of the light emitting diode. The second feedback circuit detects a driving voltage of the LED in order to prevent power loss of a transistor when a voltage is determined by feedback due to an error of the LED and a change in voltage according to temperature when a load is an LED.
At this time, the second feedback circuit determines a driving voltage. The first feedback circuit provides over voltage protection to protect the LED by detecting the opening of the LED or an over voltage of the DC/DC converter.
According to the related art, the LED driving circuit includes the first and second feedback circuits that perform a feedback function and each have an error amplifier, that is, two error amplifiers, which increases the number of components of the driving circuit. Therefore, manufacturing costs are increased, and a control circuit is more susceptible to malfunction.